1. Field of the Invention
The present general inventive concept relates to a humanoid robot. More particularly, the present general inventive concept relates to a humanoid robot capable of improving power transmission efficiency and movement displacement by modifying a wrist joint of the humanoid robot.
2. Description of the Related Art
Robots are extensively used in various industrial and domestic fields. As a result, research and development concerning humanoid robots has accelerated in recent years. In order to enable a humanoid robot to perform housework in a manner done by a human hand, for example, a humanoid robot must be able to safely and rapidly grip and handle various objects of varying sizes used by human beings.
Since the size of a robot hand is limited in a humanoid robot, many motors having large capacity may not be installed for the hand of the humanoid robot. For this reason, the robot hand tends to represent relatively low gripping force as compared with the gripping force of a human hand. In addition, since there are structural limitations in the use of a robot hand, the degree of freedom of movement of the robot hand has been very low as compared with the gripping force of the human hand.
In order to increase the gripping force of a robot hand, a motor can be installed in an arm part near the forearm, apart from the robot hand, to transfer a driving force of the motor to the fingers using wires. The wires extend by passing through a wrist joint that connects the hand to the forearm part. In order to reduce friction when the wires pass through the wrist joint, the wires are supported by two pulleys.
However, if the wrist joint is moved, the two pulleys are also moved, so that the length of the wires supported by the two pulleys may be altered. If the length of the wires are changed, the fingers may not be precisely controlled by the wires. Since the movement of the wrist joint exerts an influence upon the length of the wires, the motor driving the wires must be thus controlled in relation to the movement of the wrist joint. As a result, the driving mechanism of the motor for controlling the fingers may be hindered due to the movement of the wrist joint.
To solve the above problem, there has been suggested a driving mechanism capable of preventing the length of the wire from being changed even if the wrist joint is moved. In such a driving mechanism, the wire passing through the wrist joint, which connects the robot hand to the forearm part, is inserted into a tube, so that the length of the wire can be constantly maintained even if the wrist joint is moved. The tube serves to keep the length of the wire unchanged regardless of the movement of the wrist joint. Since the length of the wire is not changed even if the wrist joint is moved, it is not necessary to control the motor driving the wire to compensate for the length of the wire.
However, one problem with the above solution is that friction may occur between the tube and the wire inserted into the tube. Such friction may cause a great loss in the driving force of the motor, and this loss may become increased as movement displacement of the wrist joint is increased. If the movement displacement of the wrist joint is increased, the tube is excessively bent so that friction between the wire and the tube is further increased. When this happens, power transmission efficiency of the motor is remarkably lowered. To solve this problem, the movement displacement of the wrist joint must be restricted.